(1) Field of the Invention
This invention relates to air mist nozzle apparatus used, for example, for spraying cooling water on to steel materials produced by a continuous casting system or for spraying liquid preparations on to crops in kitchen gardens or orchards.
(2) Description of the Prior Art
Spray nozzle apparatus employ a method of atomizing liquid either by pressurizing it or by mixing it with air. The former method produces linear cross-sectional spray patterns, or thin water screens where the liquid is water. Therefore, when spraying water on to hot steel plate, for example, water will hit the plate in linear forms and its cooling efficiency is low. Furthermore, this method cannot make effective use of evaporation heat in that it cannot produce fine water particles which would readily evaporate upon contact with the hot plate. Large particles of water tend to rebound from the plate and therefore stay in contact with the plate only for a very short time, which does not produce a good cooling effect.
On the other hand, the latter method atomizes liquid well and produces oval cross-sectional spray patterns which have large areas of contact with the steel plate thereby producing a good cooling effect. Water is sprayed in fine particles according to this method, which will readily evaporate upon contact with the plate, and therefore efficient cooling may be carried out with a small amount of water. Fine particles of water will not rebound from the plate, but the spraying air will flow almost along the plate surface to help to maintain the sprayed water in contact with the steel plate for a long time, thereby to produce a good cooling effect. It is known that in the case of spraying liquid preparation the better the atomization, the better is the insect killing rate.
As will be understood from the above, it is an accepted fact that the method of atomizing liquid through mixture with gas is the better suited than the other for cooling steel plates and for spraying liquid preparations.
Nozzle apparatus of the air mist type are in wide use in recent times. They include, for example, a nozzle apparatus as disclosed in the Federal Republic of Germany Pat. No. 2,816,441, which is described now with reference to FIG. 13 of the accompanying drawings.
This apparatus comprises a jet pipe 102 connected to a nozzle tip 101 defining an air mist spraying orifice 101' at an end thereof. The jet pipe 102 contains a liquid supply pipe 103 fixed coaxially thereto to jet out liquid toward the orifice 101'. A gas supply pipe 106 is connected to a base end portion of the jet pipe 102 to jet out gas into a tubular space 105 defined between the jet pipe 102 and the liquid supply pipe 103 and communicating with a gas/liquid mixing space 104 in the jet pipe 102.
The nozzle apparatus of this air mist type has a disadvantage that the spray hardly diverges from an axis corresponding to the center of the nozzle tip in a symmetrical manner. This is because the gas is not under even pressure around the liquid supply pipe 103 when mixing with the liquid leaving the pipe 103. Therefore, to obtain a substantially uniform gas pressure around the end of the liquid supply pipe 103, the apparatus has a long distance from the gas supply pipe 106 to where the gas and liquid mix with each other, or the forward end of the liquid supply pipe 103.
However, such a solution requires a long double pipe portion formed of the jet pipe 102 and the liquid supply pipe 103. More particularly, since the tubular space 105 has a uniform area in the axial direction which presents no throttling action, it is necessary to insert a maximum length of the liquid supply pipe 103 in the jet pipe 102 in order to obtain a uniform peripheral pressure of the gas jetted from the tubular space 105 into the gas/liquid mxing space 104. Furthermore, the gas/liquid mixing space must have a great axial length in order to atomize the liquid positively because the liquid and gas are delivered to the gas/liquid mixing space in parallel streams. The entire nozzle apparatus therefore has to be large size and is limited in application by reason of requiring a large installation space. Moreover, since a considerable length of the liquid supply pipe 103 has to be inserted as described, a high technical level and a high degree of precision are required for aligning the forward end of the liuqid supply pipe 103 and the air mist jet pipe 102. This, together with the large size of the entire apparatus, tends to raise the manufacturing cost.
FIG. 14 shows results of tests carried out on the described nozzle apparatus of double pipe construction in respect of spray divergence. The results show that its spray patterns are not symmetric about the center of the nozzle tip.